Here’s a good explanation of why you use a child theme:
Creating a child theme when performing adjustments to your theme’s code can save you a lot of future headache. Child themes allow you to make changes without affecting the original theme’s code, which makes it easy to update your parent theme without erasing your changes. By creating a child theme, you create a separate set of files that you can use to customize the theme without affecting the original theme at all. Not only does this make updating easier, it also makes sure that you will never ruin your original theme as you are never actually modifying the files. You can always turn off your child theme and fall back on the original.
Creating a child theme with Hueman is pretty easy:
1. In Theme Options click the Help tab in the upper righthand corner.
2. One of the options in the list is to download a sample child theme. This downloads the theme zip file to your local computer.
3. Install the new theme in your Admin panel by selecting Add New > Upload Theme > Choose File, then select the zip file you downloaded.
4. Activate the child theme.
You’ll now have a pre-configured child theme with a style.css file and functions.php file to which you can add customizations. You would copy the file as I indicated above and make the change in the file in your child theme.